The present invention relates to a method of treating substrates, in particular substrates having a hard surface such as ceramics, to render them water, oil, stain and dirt repellent. The present invention also relates to compositions for use in such a method.
The use of fluorinated silanes, i.e. silane compounds that have one or more fluorinated groups for rendering substrates such as glass and ceramics oil and water repellent have been long known. For example such silanes have been described in U.S. Pat. No. 5,274,159. This latter document describes destructable fluorinated alkoxysilane surfactants that can be applied from an aqueous solution.
Commercial products are also available that comprise a silane having one or more hydrolysable groups and at least one non-hydrolysable fluorinated alkyl group. One such commercially available product is FC 405, available from 3M Company. This product comprises a solution in ethanol of a silane having a non-hydrolysable fluorinated alkyl group. The product is used to treat ceramic or glass surfaces and is generally applied in the presence of an acid such as acetic acid. Although good results are obtained with such products, there continues to be a desire to further improve them, in particular the abrasion resistance.
Fluorinated polyether silanes are also known in the art. For example, EP 789050 discloses the use thereof for making composite film coatings. U.S. Pat. No. 3,646,085 teaches fluorinated polyether silanes for rendering glass or metal surfaces oil and water repellent. The surfaces are rendered oil and/or water repellent by treating them with a solution of the fluorinated polyether silane in ethanol or in 1,2,2-trichloro-1,1,2-trifluoroethane. WO 99/37720 discloses fluorinated polyether silanes for providing an antisoiling coating to antireflective surfaces on substrates such as glass or plastic. It is taught to apply the fluorinated polyether silane from a solution in an aprotic solvent. The necessary amount of water for the condensation reaction is supplied by allowing the treated substrates to cure in an environment of sufficient humidity.
U.S. Pat. No. 3,950,588 discloses the use of fluorinated polyether silanes to render ceramic surfaces such as bathroom tiles or cookware water and/or oil repellent. It is taught in this document that care should be taken that the coating composition is contained in an anhydrous state prior to application. Also, it is recommended in this document that the surface to be treated be free of water as a separate phase. The necessary water for the polycondensation reaction at the surface is derived from adsorbed water in the ceramic and/or the environment.
Although many fluorinated silane compositions are known in the art for treating substrates to render them oil and water repellent, there continues to be a desire to provide further compositions for the treatment of substrates, in particular substrates having a hard surface such as ceramics, in order to render them water and oil repellent. Desirably, such compositions and methods employing them can yield coatings that have improved properties. In particular, it would be desirable to improve the durability of the coating, including an improved abrasion resistance of the coating. The compositions can preferably be applied in an easy, convenient and safe way and are compatible with existing manufacturing methods. Preferably, the compositions will fit easily in the manufacturing processes that are practiced to produce the substrates to be treated. The compositions preferably also avoid the use of ecologically objectionable components.
The present invention provides in one aspect a composition for treating a substrate comprising a homogeneous mixture of
(a) a fluorinated polyether silane of the formula:
Rf1xe2x80x94[xe2x80x94Qxe2x80x94SiY3xe2x88x92xR1x]yxe2x80x83xe2x80x83(I)
xe2x80x83wherein Rf1 represents a monovalent or divalent polyfluoropolyether group, Q represents an organic divalent linking group, R1 represents a C1-C4 alkyl group, Y represents a hydrolysable group; x is 0 or 1 and y is 1 or 2;
(b) an organic or an inorganic acid;
(c) water; and
(d) an organic solvent.
It has been found that when a fluorinated polyether silane of formula (I) is applied from a homogeneous mixture that includes an organic or inorganic acid as well as water, oil and water repellent coatings can be obtained that have improved abrasion resistance relative to similar fluorinated polyether silanes that have been applied in accordance with the methods of the prior art that use compositions that do not include water and the acid. Furthermore, the compositions spread well on the substrate to be treated with the result that uniform properties can be achieved over the whole surface of the treated substrate.
By the term xe2x80x98homogeneous mixturexe2x80x99 in connection with the present invention is meant that the composition is stable, i.e. no precipitation or phase separation occurs, for at least the amount of time necessary to prepare the composition and to apply it to the substrate. Generally, this means that the composition should be stable for at least one hour. Compositions of the invention were found to have generally a stability of 1 to 3 days or even longer despite the fact that the compositions contain water as well as an acid catalyst. The compositions suitable for use in this invention may be clear solutions as well as somewhat turbid mixtures.
Advantageously, the compositions of the invention are prepared by diluting a concentrated solution of the fluorinated polyether silane of formula (I). Accordingly, in a further aspect, the invention provides a method for making a composition for the treatment of a substrate, the method comprising diluting a concentrated solution of at least 25% by weight of a fluorinated polyether silane of formula (I) in an organic solvent by adding to said solution an organic solvent, water, and an organic or inorganic acid so as to prepare a homogeneous mixture containing between 0.01 and 5% by weight inclusive of the fluorinated polyether silane.
In a still further aspect, the present invention also provides a method for treating a substrate, comprising the step of applying the composition of the invention as defined above to the substrate. Preferably, the obtained coating on the substrate is cured, generally at an elevated temperature of 40 to 300xc2x0 C. The heat for curing can be supplied either through an initial preheat of substrates having sufficient heat capacity to provide the heat for curing, or through heating of coated substrates by an external heat source subsequent to coating.
The monovalent or divalent polyfluoropolyether group Rf in the above Formula I, representing the fluorinated polyether silane, can include linear, branched, and/or cyclic structures, that may be saturated or unsaturated. It is preferably a perfluorinated group (i.e., all Cxe2x80x94H bonds are replaced by Cxe2x80x94F bonds). More preferably, it includes perfluorinated repeating units selected from the group of xe2x80x94(CnF2n)xe2x80x94, xe2x80x94(CnF2nO)xe2x80x94, xe2x80x94(CF(Z))xe2x80x94, xe2x80x94(CF(Z)O)xe2x80x94, xe2x80x94(CF(Z)CnF2nO)xe2x80x94, xe2x80x94(CnF2nCF(Z)O)xe2x80x94, xe2x80x94(CF2CF(Z)O)xe2x80x94, and combinations thereof. In these repeating units Z is a perfluoroalkyl group, an oxygen-substituted perfluoroalkyl group, a perfluoroalkoxy group, or an oxygen-substituted perfluoroalkoxy group, all of which can be linear, branched, or cyclic, and preferably have about 1 to about 9 carbon atoms and 0 to about 4 oxygen atoms. Examples of polyfluoropolyethers containing polymeric moieties made of these repeating units are disclosed in U.S. Pat. No. 5,306,758 (Pellerite). For the monovalent polyfluoropolyether group (wherein y is 1 in Formula I above), the terminal groups can be (CnF2n+1)xe2x80x94, (CnF2n+1O)xe2x80x94 or (Xxe2x80x2CnF2nO)xe2x80x94, wherein Xxe2x80x2 is H, Cl, or Br, for example. Preferably, these terminal groups are perfluorinated. In these repeating units or terminal groups, n is I or more, and preferably 1 to 4.
Preferred approximate average structures for a divalent perfluoropolyether group include xe2x80x94CF2O(CF2O)m(C2F4O)pCF2xe2x80x94, wherein an average value for m and p is 0 to 50, with the proviso that m and p are not simultaneously 0, xe2x80x94CF(CF3)O(CF(CF3)CF2O)pCF(CF3)xe2x80x94, xe2x80x94CF2O(C2F4O)pCF2xe2x80x94, and xe2x80x94(CF2)3O(C4F8O)p(CF2)3xe2x80x94, wherein an average value for p is 1 to 50. Of these, particularly preferred approximate average structures are xe2x80x94CF2O(CF2O)m(C2F4O)pCF2xe2x80x94, xe2x80x94CF2O(C2F4O)pCF2xe2x80x94, and xe2x80x94CF(CF3)O(CF(CF3)CF2O)pCF(CF3)xe2x80x94. Particularly preferred approximate average structures for a monovalent perfluoropolyether group include C3F7O(CF(CF3)CF2O)pCF(CF3)xe2x80x94 and CF3O(C2F4O)pCF2xe2x80x94 wherein an average value for p is 1 to 50. As synthesized, these compounds typically include a mixture of polymers. The approximate average structure is the approximate average of the mixture of polymers.
The divalent linking group Q can include linear, branched, or cyclic structures, that may be saturated or unsaturated. The group Q can contain one or more heteroatoms (e.g., oxygen, nitrogen, or sulfur) or functional groups (e.g., carbonyl, amido, urethanylene or sulfonamido). It can also be substituted with halogen atoms, preferably, fluorine atoms, although this is less desirable, as this might lead to instability of the compound. Preferably, the divalent linking group Q is a hydrocarbon group, preferably, a linear hydrocarbon group, optionally containing heteroatoms or functional groups, and more preferably, containing at least one functional group. Examples of Q groups include xe2x80x94C(O)NH(CH2)3xe2x80x94, xe2x80x94CH2O(CH2)3xe2x80x94, xe2x80x94C(O)S(CH2)3xe2x80x94, xe2x80x94CH2OC(O)N(R)(CH2)3xe2x80x94, wherein R is H or lower alkyl group, and xe2x80x94(CnH2n)xe2x80x94, wherein n is about 2 to about 6. A preferred linking group Q is xe2x80x94C(O)NH(CH2)3xe2x80x94 or xe2x80x94CH2O(CH2)3xe2x80x94.
Y represents a hydrolyzable group in formula (I) such as for example a halide, a C1-C4 alkoxy group, an acyloxy group or a polyoxyalkylene group, such as polyoxyethylene groups as disclosed in U.S. Pat. No. 5,274,159. Specific examples of hydrolysable groups include methoxy, ethoxy, propoxy, chloro, and acetoxy groups.
Compounds of Formula I suitable for compositions for treating substrates of the present invention have a molecular weight (number average) of at least about 200, and preferably, at least about 1000. Preferably, they are no greater than about 10000.
Examples of preferred fluorinated silanes include, but are not limited to, the following approximate average structures: XCF2O(CF2O)m(C2F4O)pCF2X, C3F7O(CF(CF3)CF2O)pCF(CF3)X, XCF(CF3)O(CF(CF3)CF2O)pCF(CF3)X, XCF2O(C2F4O)pCF2X, and CF3O(C2F4O)pCF2X, X(CF2)3O(C4F8O)p(CF2)3X, wherein xe2x80x94X is xe2x80x94Qxe2x80x94SiY3xe2x88x92xRx1 as defined above in Formula I or a nonsilane-containing terminal group as defined above ((CnF2n+1)xe2x80x94, (CnF2n+1O)xe2x80x94 or (Xxe2x80x2CnF2nO)xe2x80x94 wherein Xxe2x80x2 is H, Cl, or Br), with the proviso that at least one X group per molecule is a silane). Preferably, in each fluorinated polyether silane, Q contains a nitrogen or oxygen atom. More preferably, at least one X group per molecule is C(O)NH(CH2)3Si(OR)3 (wherein R is methyl, ethyl, polyethyleneoxy or mixtures thereof), and the other X group, if not a silane, is OCF3, or OC3F7. The values of m and p in these approximate average structures can vary. Preferably, an average value of m is within a range of about 1 to about 50, and an average value of p is within a range of about 4 to about 40. As these are polymeric materials, such compounds exist as mixtures upon synthesis, which are suitable for use. These mixtures may also contain perfluoropolyether chains bearing no functional groups (inert fluids) or more than two terminal groups (branched structures) as a consequence of the methods used in their synthesis. Typically, mixtures of polymeric materials containing less than about 10% by weight of nonfunctionalized polymers (e.g., those without silane groups) can be used. Furthermore, mixtures of any of the individually listed compounds of Formula I can be used.
The compounds of Formula I can be synthesized using standard techniques. For example, commercially available or readily synthesized perfluoropolyether esters can be combined with a functionalized alkoxysilane, such as a 3-aminopropylalkoxysilane, according to U.S. Pat. No. 3,810, 874 (Mitsch et al.), incorporated herein by reference. Modifications of this method are described in the Examples. Such materials may or may not need to be purified before use in a treatment composition.
The composition comprising the fluorinated polyether silane of formula (I) is generally applied to the substrate in amounts sufficient to produce a coating which is water and oil repellent. This coating can be extremely thin, e.g. 1 to 50 molecular layers, though in practice a useful coating may be thicker.
Although the inventors do not wish to be bound by theory, compounds of the above Formula I are believed to undergo reaction with the substrate surface to form a siloxane layer. For the preparation of a durable coating, sufficient water should be present in order to cause hydrolysis of the silane end groups, and then condensation of the resulting silanol groups on and to the substrate. In this context, xe2x80x9csiloxanexe2x80x9d refers to Sixe2x80x94Oxe2x80x94Sixe2x80x94 bonds to which are attached polyfluoropolyether segments (such as the Rf1 groups in Formula I herein), preferably, perfluoropolyether segments, bonded to the silicon atoms through organic linking groups (such as the Q groups in Formula I herein). In particularly preferred embodiments, the Q groups include nitrogen atoms (as in an amido group). A coating prepared from a coating composition that includes compounds of Formula I can also include unreacted or uncondensed silanol groups.
To achieve good durability, the compositions of the present invention include water. Typically, the amount of water will be between 0.1 and 20% by weight, preferably between 0.5% by weight and 15% by weight, more preferably between 1 and 10% by weight.
In addition to water, the compositions of the invention preferably include an organic or inorganic acid. Organic acids include acetic acid, citric acid, formic acid and the like; fluorinated organic acids, such as CF3SO3H, C3F7COOH, C7F15COOH, C6F3P(O)(OH)2, or those which can be represented by the Formula II
Rf2xe2x80x94[xe2x80x94(L)mxe2x80x94Z]nxe2x80x83xe2x80x83(II)
wherein Rf2 represents a mono or divalent polyfluoropolyether group, L represents an organic divalent linking group, Z represents an acid group, such as carboxylic acid group; m is 0 or 1 and n is 1 or 2.
Examples of suitable Rf2 groups include those given above for R1f. Examples of organic acids of Formula II include C3F7O(CF(CF3)CF2O)10-30CF(CF3)COOH, commercially available from DuPont as 157 FSH, 157 FSL, and 157 FSM, or CF3(CF2)2OCF(CF3)COOH.
Examples of inorganic acids include sulphuric acid, hydrochloric acid, phosphoric acid, and the like. The acid will generally be included in the composition in an amount between about 0.005 and 10%, more preferably between 0.05 and 5% by weight.
A composition of the present invention includes one or more organic solvents. The organic solvent or blend of organic solvents used must be capable of dissolving at least 0.01% by weight of the fluorinated polyether silane of Formula I. Furthermore, the solvent or mixture of solvents must have a solubility for water of at least 0. 1% by weight and a solubility for acid of at least 0.01% by weight. If the organic solvent or mixture of organic solvents do not meet these criteria, it may not be possible to obtain a homogeneous mixture of the fluorinated silane, solvent(s), water and acid. Although such non-homogeneous compositions could be used to treat a substrate, the coating obtained therefrom will generally not have the desired oil/water repellency and will not have sufficient durability properties.
Suitable organic solvents, or mixtures of solvents can be selected from aliphatic alcohols, such as methanol, ethanol, isopropyl alcohol; ketones such as acetone or methyl ethyl ketone; esters, such as ethyl acetate, methylformate and ethers, such as diisopropyl ether. Fluorinated solvents may be used in combination with the organic solvents in order to improve solubility of the fluorinated polyether silane. Such fluorinated solvents will generally not be suitable for use on their own because they will generally not meet the requirements of solubility for water and acid.
Examples of fluorinated solvents include fluorinated hydrocarbons, such as perfluorohexane or perfluorooctane, available from 3M; partially fluorinated hydrocarbons, such as pentafluorobutane, available from Solvay, or CF3CFHCFHCF2CF3, available from DuPont; and hydrofluoroethers, such as methyl perfluorobutyl ether or ethyl perfluorobutyl ether, available from 3M. Various blends of these materials with organic solvents can be used.
The compositions may contain further components such as, for example, hydrocarbon silanes, i.e. silanes that are substantially non-fluorinated. However, the addition of hydrocarbon silanes is preferably kept below about 1% by weight, in order not to adversely affect the oil repellency properties of the composition.
Suitable substrates that can be treated in a particularly effective way with the fluorinated polyether silane mixture of this invention include substrates having a hard surface preferably with functional groups capable of reacting with the fluorinated silane according to formula (I). Preferably, such reactivity of the surface of the substrate is provided by active hydrogen atoms. When such active hydrogen atoms are not present, the substrate may first be treated in a plasma containing oxygen or in a corona atmosphere to make it reactive to the fluorinated polyether silane. Particularly preferred substrates include ceramics, glazed ceramics, glass, metal, natural and man-made stone, thermoplastic materials (such as poly(meth)acrylate, polycarbonate, polystyrene, styrene copolymers, such as styrene acrylonitrile copolymers, polyesters, polyethylene terephthalate), paints (such as those based on acrylic resins), powder coatings (such as polyurethane or hybrid powder coatings), and wood. Various articles can be effectively treated with the fluorochemical solution of the present invention to provide a water and oil repellent coating thereon. Examples include ceramic tiles, bathtubs or toilet pots, glass shower panels, construction glass, various parts of a vehicle (such as the mirror or windscreen), glass, and ceramic or enamel pottery materials.
Treatment of the substrates results in rendering the treated surfaces less retentive of soil and more readily cleanable due to the oil and water repellent nature of the treated surfaces. These desirable properties are maintained despite extended exposure or use and repeated cleanings because of the high degree of durability of the treated surface as can be obtained through the compositions of this invention.
Preferably, the substrate should be clean prior to applying the compositions of the invention so as to obtain optimum characteristics, particularly durability. That is, the surface of the substrate to be coated should be substantially free of organic contamination prior to coating. Cleaning techniques depend on the type of substrate and include, for example, a solvent washing step with an organic solvent, such as acetone or ethanol. The coating composition is typically a relatively diluted solution, containing between 0.01 and 5 percent by weight inclusive of the fluorinated silane, more preferably, between 0.03 and 3 percent by weight inclusive of the fluorinated silane, and most preferably, between 0.05 and 0.2 percent by weight inclusive of the fluorinated polyether silane. The ratio of the solvents, water and acid should be chosen so as to obtain a homogeneous mixture.
For ease of manufacturing and for reasons of cost, the compositions of the present invention will generally be prepared shortly before use by diluting a concentrate of the fluorinated polyether silane of formula (I). The concentrate will generally comprise a concentrated solution of the fluorinated polyether silane of formula (I) in an organic solvent without water and/or acid being present in such concentrate. The concentrate should be stable for several weeks, preferably at least 1 month, more preferably at least 3 months. It has been found that the fluorinated polyether silane of formula (I) can be readily dissolved in an organic solvent at high concentrations. Fluorinated polyethers of molecular weight lower than about 1000 give clear solutions in many organic solvents such as alcohols, ketones, and esters over a wide range of concentrations. For fluorinated polyethers of molecular weight higher than about 1,500, a surprising solubility effect has been found. Particularly, it was found that at amounts of at least 25% by weight, it becomes easier to dissolve the fluorinated polyether silane (I) in an organic solvent and obtain concentrated solutions that are generally clear and stable over a long period. This is surprising as only turbid solutions of limited stability may be obtained at low concentration, whereas at high concentration in the same organic solvent, clear solutions with high stability are obtained. For example, at room temperature, stable clear solutions of these higher molecular weight materials can be obtained in ketones ) (e.g., acetone, methyl ethyl ketone, and methyl isobutyl ketone), esters (e.g., ethyl acetate), and alcohols (e.g., ethanol, methanol, and isopropanol) at a concentration of at least 25% by weight of the fluorinated polyether silane (I), whereas at a concentration of only 0.1% in non-halogenated organic solvents, the solution tends to be hazy and of limited stability. In ethanol, it was found that clear stable solutions were formed at concentrations of at least 40% by weight whereas at 0.1% by weight, the solution was hazy. On the other hand in highly fluorinated solvents, such as hydrofluoroethers, hydrofluorocarbons, or perfluorocarbons, solutions containing 0.1% or more of the fluorinated polyether silane, are clear.
Thus, in accordance with a preferred embodiment, compositions for application to a substrate are prepared by diluting a concentrate comprising a solution of at least 25% by weight of a fluorinated polyether silane according to Formula I in an organic solvent, by adding to the concentrate an organic solvent or mixture of solvents, water, and an organic acid. A thus freshly prepared diluted solution will generally be stable for 1 or more days. It has further been found that conditioning the composition at room temperature for 1 to 3 days may further improve the abrasion resistance of a coating prepared from such a conditioned solution.
A wide variety of coating methods can be used to apply a composition of the present invention, such as brushing, spraying, dipping, rolling, spreading, and the like. A preferred coating method for application of a fluorinated polyether silane mixture of the present invention includes spray application. A substrate to be coated can typically be contacted with the treating composition at room temperature (typically, about 20xc2x0 C. to about 25xc2x0 C.). Alternatively, the mixture can be applied to substrates that are preheated at a temperature of for example between 60xc2x0 C. and 150xc2x0 C. This is of particular interest for industrial production, where eg. ceramic tiles can be treated immediately after the baking oven at the end of the production line. Following application, the treated substrate can be dried and cured at ambient or elevated temperature, e.g. at 40xc2x0 to 300xc2x0 C. and for a time sufficient to dry. The process may also require a polishing step to remove excess material.